Red blood cells, platelets, and white blood cells are suspended in the plasma of peripheral blood. Specimens are frequently examined since a great deal of clinical information can be obtained by blood analyses that examine these cells.
Basic items in blood examinations include measurement of the number of red blood cells, number of platelets, number of white blood cells, and hemoglobin concentration in the blood, and a hematocrit value is determined from these measurement results. The measurement of these values is generally referred to as CBC (complete blood count), and hemocytometers are widely used to determine CBC.
Hemocytometers allocate a blood sample into a plurality of aliquots. For example, a first aliquot may be diluted with a dilution liquid and used to measure the red blood cell count and platelet count. A second aliquot may be added with a hemolytic agent to hemolyze the red blood cells and used to measure white blood cells. A third aliquot may be used to measure hemoglobin concentration by adding a hemolytic agent to release the hemoglobin in the red blood cells. A hemocytometer performs these measurements and determines the hematocrit value.
The measurement of a white blood cell count is added to a white blood cell classification examination in order to provide clinical information more sophisticated than CBC, and the white blood cell classification examinations are widely performed to classify white blood cells as lymphocytes, monocytes, neutrophils, eosinophils, and basophils.
White blood cell classification methods classify white blood cells based on optical signals or electrical signals of scattered light, fluorescent light and so on, or combinations thereof, using stains to stain particles and hemolytic agents capable of preserving the cellular morphology of the white blood cell.
An example of a hemocytometer capable of white blood cell classification is the model XE-2100 manufactured by Sysmex Corporation.
The XE-2100 allocates a blood sample into a blood for measurement of a red blood cell count and platelet count, blood for measurement of hemoglobin concentration, and blood for measurement of white blood cell. The XE-2100 further allocates the blood for measurement of white blood cell into two aliquots; a WBC count reagent is added to one aliquot and the number of white blood cells and number of basophils are counted, and a WBC classifying reagent is added to the other aliquot and the white blood cells are classified into four classification types, and both of these measurement results are used as the basis for the white blood cell count and the white blood cell classifications.
The XE-2100 is configured so as to be capable of operating in a first mode that measures the white blood cell count, but does not classify the white blood cells, and a second mode that measure the white blood cell count and classifies the white blood cells. The XE-2100 requires two aliquots to measure the white blood cell count and perform the white blood cell classification in the second mode. Furthermore, since white blood cell classification is generally performed less frequently than measurement of the white blood cell count, the special reagent required for white blood cell classification in conventional hemocytometers is wasted when the white blood cell classification reagent use period expires.
U.S. Pat. No. 5,656,499 also discloses another hemocytometer. This hemocytometer has a plurality of mixing chambers for preparing mixed preparations corresponding to a plurality of aliquots. A first aliquot is subjected to hemolytic processing and thereafter scattered light from the cells is detected at multiple angles using an optical flow cell/transducer to measure the number of white blood cells and perform white blood cell classification. A second aliquot is subjected to dilution processing and thereafter the change in impedance when the cells pass through an orifice is detected by an impedance transducer to measure the red blood cell count and platelet count. A third aliquot is subjected to hemolytic processing and thereafter the light optical density of the hemolytic sample is detected by an HGB (hemoglobin) transducer to measure the HGB concentration.